A highly conventional and widely used method of packaging utilizes a peelable laminated lid material which has been adhered to a rigid container. The lid material is typically made from a backing material coated with a heat sealable material which can be easily peeled. The backing material may be any material strong enough to close said container and also to provide any barrier properties which may be needed. The backing material may be for example; metal foil, polypropylene film, polyester film, nylon film, paper, etc. In many instances, it is desirable to open the package by peeling off the lid material, and this must generally be done without destroying the integrity of the film itself. Accordingly, to provide a satisfactory package of this type, a balance of properties is necessary, i.e. the seal strength must be adequate to maintain the package in a closed and protective condition, while also exhibiting release properties as will permit opening by peeling when desired. In the past there has been no inexpensive effective means to use peel seal closures with rigid styrenic containers or with PVC-based containers because a single peelable adhesive could not be used with olefinic rigid containers as well as styrenic and PVC based containers.
The invention relates to blends, and a method for making a blend usable in a flexible film package made from films and/or laminates and rigid containers using said film or laminate as a closure. Seals produced from these heat-sealable films and/or laminates are characterized by an adequate, nearly constant peel strength when used on rigid containers including styrenic containers and PVC containers. The seals can be formed over a wide range of heat seal temperatures and are easily peelable. The term peelable refers to a film having seal failure occur primarily at the interface of the sealing surfaces, rather than film tearing. The blends, films and/or laminates of the present invention permit the manufacture of a seal which will adhere to a variety of substrates including styrenic, PVC, and olefinic rigid containers.
Most of the commercial peel seal materials are polyolefin based copolymers that can not be used for polystyrene or PVC containers since there is no adhesion between these two types of polymers.
At the present time, in order to use the easy open, peelable lid concept on polystyrene or PVC rigid containers, the manufacturer must coextrude polystyrene with high density polyethylene (HDPE) to form the containers so that the HDPE surface can be sealed with peel seal material. This is a costly process.
One type of peel seal material currently available for polystyrene containers is ethylene/vinyl acetate (EVA) based liquor. The process involves venting and recovering of organic solvent and EVA often produces organoleptic problems in food which is packaged in such containers.
A variety of references teach heat sealable films capable of forming peel seals, such as U.S. Pat. Nos. 4,550,141; 4,539,263; 4,414,053 and 3,879,492. However, none of these references appear to teach a composition which will perform as a peelable seal to rigid styrenic, PVC, or olefinic containers.
The instant invention is a novel blend, method of making a film and a peel sealable package which creates chemically compatible backing materials and peelable sealants useful for polystyrene, PVC, or olefinic containers. The invention thus provides a blend which will provide a peelable seal which can be used on a wide variety of rigid containers which in the past required two or more peelable seal compositions.